1. Field of the Invention
The present invention relates to a diagnosis apparatus for diagnosing a variable valve timing mechanism, more particularly to a diagnosis apparatus for diagnosing a variable valve timing mechanism which switches a phase of a cam shaft of an internal combustion engine with respect to a crank shaft in correspondence to an operational condition and switches an open and close timing of an intake and/or exhaust valve in correspondence to the operational condition, in which whether or not the switching of the phase is normally performed is diagnosed.
2. Description of the Related Art
A conventional diagnosis apparatus in a variable valve timing mechanism which switches a phase between a crank shaft and a cam shaft so as to control an open and close timing of an intake and/or exhaust valve is disclosed in Japanese Patent Application Laid-Open No.4-112908.
The apparatus is provided with a sensor for detecting a predetermined angular position of the crank shaft, a sensor for detecting a predetermined angular position of the cam shaft, and is structured such as to calculate a phase difference of a crank angle between the crank shaft and the cam shaft on the basis of detected signals from these sensors and to diagnose a fault on the basis of a fact that whether or not the phase difference of the crank angle becomes a value corresponding to a control state of the variable valve timing mechanism.
In the above-described conventional diagnosis apparatus, if there is an error in the detected position detected by the sensor for detecting the crank angle and the sensor for detecting the phase of the cam shaft, a dispersion occurs in the detected phase difference so that there is a fear that a fault is erroneously diagnosed because the predetermined phase difference is not obtained even when the mechanism is normally operated or inversely a normal operation is erroneously diagnosed even when the predetermined phase difference is not obtained. Accordingly, there is a problem that it is difficult to accurately diagnose an error of a small phase angle.